Communications method and system

ABSTRACT

A communications system comprising a first plurality of cells operating in accordance with a first mode and a second plurality of cells operating in accordance with a second mode, each of said cells being served by a respective first station, at least one second station arranged to establish a connection with at least one first station, said at least one second station being associated with said first plurality of cells or said second plurality of cells during said connection and means for determining which plurality of cells said second station is associated after said connection has been completed.

FIELD OF THE INVENTION

[0001] The present invention relates to a communications system andmethod. In particular, but not exclusively, the present inventionrelates to a dual mode wireless cellular communications system.

BACKGROUND OF THE INVENTION

[0002] In known wireless cellular telecommunication networks, an areacovered by a network is divided into a plurality of cells. Each of thesecells has a base station which is arranged to transmit signals to andreceive signals from mobile stations located in the cell associated withthe respective base station. Mobile stations will be in activecommunication with the base station associated with the cell in whichthe mobile station is located.

[0003] A number of different cellular telecommunication standards areused or have been proposed. One such standard is the GSM (Global Systemfor Mobile Communications) standard. GSM uses a frequency/time divisionmultiple access technique. A mobile station is allocated a givenfrequency band and time slots in order to transmit to the base station.The mobile station is allocated a different frequency band and timeslots to receive signals from the base station. The allocated frequencyband and time slots can be changed over time.

[0004] There are a number of different frequency bands at which GSM canbe used. For example, one frequency is around 900 MHz. This will bereferred to as GSM 900. Another frequency is around 1800 MHz This willbe referred to as GSM 1800.

[0005] A third generation standard has been proposed and is referred toas UMTS (Universal Mobile Telecommunications System). UMTS uses a codedivision multiple access technique. With the proposed UMTS system, softhandoff has been proposed. With soft handoff, a mobile station is incommunication with more than one base station at the same time.

[0006] It is possible that networks using different standards can coverthe same area. As the different standards use different methods ofaccess and/or different frequencies, the different networks do notinterfere. Multiband mobile phones operate on more than one frequencyband of the same standard. Dual mode mobile phones have been proposedparticularly in the context of the GSM and UMTS standards. Accordingly,one dual mode mobile station is able to communicate with a network usingthe GSM standard and a network using the UMTS standard. A multibandmobile station is able to communicate e.g. either on a GSM 900 networkor on a GSM 1800 network. At any one time the mobile station will beconnected to only one network. In the GSM standard, it is stated thatwhen a mobile station completes a connection and is in an idle mode, themobile station camps on the cell whose channel has been released. Inother words, the mobile station remains associated, in the idle mode,with the cell with which it has just completed a connection. This issometimes disadvantageous in that the cell with which the mobile stationis associated may not be the most appropriate cell. In order to changethe cell with which the mobile station is associated or camping on, acell reselection procedure has to be carried out. This can be acomplicated procedure especially if the mobile station is changing fromone network to another. A network operator requires extensive experiencein parameter setting.

[0007] In the GSM standard, parameters are defined for the cellre-selection procedure. With these parameters, which are set by theoperator and broadcast on the BCCH/PBCCH of the cell, the mobile stationis able to find out, which cell should be considered as the best celland whether a cell re-selection shall be proceed.

[0008] These parameters are, for example, offsets to the measured signalstrengths of the serving cell and neighbour cells to get the mobilestation to camp on the wanted cell. The wanted cell may also belong to adifferent location area compared to the cell where the connection wasreleased. Assuming that the call was initiated in one network (e.g. GSM900) but the mobile station was handed over to another network (e.g.UMTS), typically the mobile station should perform a location updateprocedure on the cell where the call was released. If then the operatorprefers mobile stations to camp on the GSM system in idle mode, then themobile station would reselect another cell from the GSM network andwould again typically perform a location update. This slows down thereselection of the intended cell and adds unnecessary signalling.

SUMMARY OF THE INVENTION

[0009] It is an aim of embodiments of the present invention to addressthe problems with the known arrangements.

[0010] According to a first aspect, there is provided a communicationssystem comprising a first plurality of cells operating in accordancewith a first mode and a second plurality of cells operating inaccordance with a second mode, each of said cells being served by arespective first station, at least one second station arranged toestablish a connection with at least one first station, said at leastone second station being associated with said first plurality of cellsor said second plurality of cells during said connection and means fordetermining which plurality of cells said second station is associatedafter said connection has been completed.

[0011] Preferably, the communications system comprises at least onenetwork to which said second station is attachable, said first stationsbeing part of said at least one network, wherein said at least onenetwork is arranged to determine the plurality of cells to which saidsecond station is to be associated.

[0012] According to a second aspect, there is provided a communicationssystem comprising a first plurality of cells operating in accordancewith a first mode and a second plurality of cells operating inaccordance with a second mode, each of said cells being served by arespective first station, at least one second station arranged toestablish a connection with at least one first station, and means forcontrolling which at least one cell said second station is associatedwhen said second station is idle.

[0013] According to a third aspect, there is provided a communicationssystem comprising a first plurality of cells operating in accordancewith a first mode and a second plurality of cells operating inaccordance with a second mode, each of said cells being served by arespective first station, at least one second station arranged toestablish a connection with at least one first station, said at leastone second station being associated with said first plurality of cellsor said second plurality of cells during said connection and means forcontrolling if the second station is associated with at least one celloperating in accordance with the first mode or at least one celloperating in accordance with the second mode, after said connection hasbeen completed.

[0014] According to a fourth aspect, there is provided a communicationsmethod for a communications system comprising a first plurality of cellsoperating in accordance with a first mode and a second plurality ofcells operating in accordance with a second mode, each of said cellsbeing served by a respective first station, said method comprising thesteps of. establishing a connection between a second station and atleast one first station; releasing the connection between the first andsecond station; and selecting if the second station is to be associatedwith a cell operating in accordance the first mode or the second mode.

[0015] According to a filth aspect of the present invention, there isprovided a communications system method for a communications systemcomprising a plurality of cells; each of said cells being served by arespective first station and at least one second station, said methodcomprising the steps of: establishing a connection between at least onefirst station and a second station, said at least one second stationbeing associated with a first cell during said connection; andcontrolling which cell said second station is associated with in idlemode after said connection has been completed.

[0016] According to a further aspect of the invention, there is provideda network element of a communications system comprising a plurality ofcells, each of said cells being served by a respective first station, atleast one second station arranged to establish a connection with atleast one first station, said at least one second station beingassociated with a first cell during said connection, said networkelement comprising means for controlling which cell said second stationis associated with in idle mode after said connection has beencompleted.

[0017] According to a further aspect of the invention, there is provideda first station of a communications system comprising a plurality ofcells, each of said cells being served by a first station, at least onesecond station arranged to establish a connection with at least onefirst station, said at least one second station being associated with afirst cell during said connection, said first station comprising meansfor controlling which cell said second station is associated with inidle mode after said connection has been completed.

[0018] According to a further aspect of the present invention, there isprovided a second station of a communications system comprising a firstplurality of cells arranged to operate in accordance with a first modeand a second plurality of cells arranged to operate in accordance with asecond mode, each of said cells being served by a first station, saidsecond station arranged to establish a connection with at least onefirst station, said second station being associated with a first cellduring said connection, said second station being arranged to receiveinformation for controlling which plurality of cells said second stationis associated.

[0019] According to a further aspect of the present invention, there isprovided a communications system comprising

[0020] a plurality of cells, each of said cells being served by arespective first station;

[0021] at least one second station arranged to establish a connectionwith at least one first station;

[0022] said at least one second station being associated with a firstcell during said connection; and

[0023] means for controlling which cell said second station isassociated with in idle mode after said connection has been completed.

BRIEF DESCRIPTION OF DRAWINGS

[0024] For a better understanding of the present invention and as to howthe same may be carried into effect, reference will now be made by wayof example only to the accompanying drawings in which:—

[0025]FIG. 1 shows two overlapping networks;

[0026]FIG. 2 shows the hierarchy of a GSM network;

[0027]FIG. 3 shows the hierarchy of a UMTS network;

[0028]FIG. 4 shows a first method embodying the present invention;

[0029]FIG. 5 shows a second method embodying the present invention; FIG.6 shows a third method embodying the present invention; and

[0030]FIG. 7 shows a fourth method embodying the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

[0031] Reference will first be made to FIG. 1, which shows a first setof cells with radio access mode 1 (cells A) and a second set of cellswith radio access mode 2 (cells B). For simplicity, the cells with radioaccess mode 1 are referred to as network A and cells with radio accessmode 2 as network B. However, it should be noted that at least parts ofnetworks A and B may be integrated. For example, the connectionmanagement function such as the mobile services switching centres MSCfor the networks may be implemented in a single mobile servicesswitching centre MSC. The networks may be separate networks or a singlenetwork which uses two different radio access technologies. As can beseen from FIG. 1, the two networks A and B cover the same area. Thefirst network A is divided into a plurality of cells 2. The secondnetwork B is also divided into a plurality of cells 4. It should beappreciated that the cells in the two networks can be the same ordifferent sizes. Likewise, the cell shapes can be the same or different.The cells of the networks may coincide or may be in different locations.

[0032] In the preferred embodiment of the present invention, network Ais in accordance with a GSM standard whilst network B is in accordancewith a UMTS standard.

[0033] However, it should be appreciated that in alternative embodimentsof the present invention, the two networks may be in accordance with anytwo standards. For example, networks A and B could be GSM 900 and GSM1800 respectively Embodiments of the present invention will be describedin the context of two overlapping networks. However, it should beappreciated that embodiments of the present invention can be used wherethere are more than two overlapping networks. It should be appreciatedthat in embodiments of the present invention, the area covered by eachnetwork may only partially overlap.

[0034] Reference is made to FIG. 2, which shows the hierarchy of theelements in network A Each cell 2 is served by a base transceiverstation 6. In FIG. 2, two base stations 6 are shown. However, it shouldbe appreciated that in practice there will be many more base stations. Amobile station 8 is arranged to communicate with the base transceiverstation of the cell in which the mobile station is currently located. Inpractice, each base transceiver station 6 will be in communication witha number of different mobile stations. The two base stations 6 shown inFIG. 2 are connected to a base station controller 10. The base stationcontroller 10 is arranged to control the two base transceiver stations6. In practice, a number of base station controllers are provided.Accordingly, neighbouring base stations may be connected to differentbase station controllers.

[0035] The base station controllers 10 are in turn controlled by amobile services switching centre MSC 12. Again, more than one mobileservices switching centre 12 are generally provided and those mobileservices switching centres 12 are arranged to communicate with eachother. The mobile services switching centre deals with circuit switcheddata, Network elements (such as a serving GPRS support node SGSN) mayalternatively or additionally deal with packet switched data. The mobileservices switching centre MSC and serving GPRS support node SGSN andgateway GPRS support node GGSN build with the home location register HLRand the visitor location register VLR a core network. Also the futurevoice over Internet protocol VolP and other Internet protocol networkscan be supported. In VolP or other lP, the functionality of a mobileservices switching centre MSC is implemented in a circuit switched callfunction CSCF.

[0036] The connection between the mobile station 8 and the associatedbase station 6 will be via a radio connection. The connection betweenthe base stations and the base station controller and between the basestation controller and the mobile services switching centre willgenerally be via wired connections although in some alternativeembodiments the connections may be wireless connections.

[0037] Reference is made to FIG. 3 which shows the elements of the UMTSnetwork B. Each cell 4 is served by a node B 14. Functionally, node B isequivalent to the base station of FIG. 2 although different terminologyis used in relation to the UMTS standard. For the purpose of thisdocument, where appropriate, the term base transceiver station should beinterpreted to cover the base transceiver station of FIG. 2 and node Bof FIG. 3 and any other functionally equivalent element.

[0038] As with the arrangement of FIG. 2, a mobile station 8 is arrangedto communicate with node B 14 via a radio connection. Each node B 14 iscontrolled by a radio network controller 16. In the arrangement shown inFIG. 3, two radio network controllers are provided. In practice, eachradio network controller 16 will control more than one node B. The radionetwork controller 16 is again functionally equivalent to the basestation controller 10. Accordingly, the term base station controller inthis document, is to be interpreted where appropriate as including thebase station controller 10 of FIG. 2 and the radio network controller 10of FIG. 3 or any other functionally equivalent element The radio networkcontrollers are each connected to a mobile services switching centre 18which is functionally similar to the mobile services switching centre 12of the GSM network.

[0039] It should be appreciated that the network shown in FIG. 3 mayalso have components to support packet switched connections, voice overInternet protocol connections and Internet protocol connections.

[0040] The mobile station 8 is a dual mode mobile station. This meansthat the mobile station is able to communicate with the GSM network orthe UMTS network. In embodiments of the present invention, the mobilestation is only connected to one of the networks at a time.

[0041] Each mobile station has effectively three different states. Inthe first state, the mobile station is off and is unable to communicatewith either of the networks In a second state, the mobile station isactively connected to a base station or node B. In this activeconnection, data is exchanged between the mobile station and the basestation or node B. This date can take the form of voice data or anyother type of data. In other words, a call is established between themobile station and the base station or node B in the third state, themobile station is not engaged in a call and is in an idle mode. However,the mobile station is still associated with one of the base stations ornode B. The embodiments of the invention which are described hereinafterare concerned with the selection of the cell with which the mobilestation is associated when the mobile station completes a call andchanges to the idle state.

[0042] Reference will now be made to FIG. 4 which shows a firstembodiment of the present invention. In step S1, the mobile station isinitially in an idle state. In step S2, the mobile station establishes aconnection to a third party.

[0043] In step S3 a network element determines the cell with which themobile station 8 is to be associated when a call connection is released.This network element will be a network element upstream of the basestation or node B with which the mobile station is currently connected.For example, in the case of a GSM network where the mobile station 8 isconnected to a base transceiver station 6, the base station controllerand/or the mobile services switching centre 12 will select the cell. Ifthe mobile station 8 is connected to node B 14 of the UTMS network, thenthe radio network controller 16 and/or the mobile services switchingcentre 18 will select the cell or the radio access technology with whichthe mobile station is to be associated when the call connection isreleased. It should be noted that it is only possible to select a cellof the network to which the mobile station is currently connected. Ifthe networks share components or communicate, then it is possible forcells of either network to be selected. If the mobile station is to beassociated with a cell of the other network, then the method of FIG. 5may be performed.

[0044] It should be appreciated that in alternative embodiments of thepresent invention, network elements may make the decision as to the cellor the radio access technology with which the mobile station is to beassociated.

[0045] Any suitable criteria may be used in order to select the cell.For example, received measurement reports may be used. The measurementreports may be signals received by the mobile station from the strongestbase stations. Alternatively, the measurement reports may be based onsignals received by the base station with which the mobile station iscurrently connected and possibly neighbouring base stations.

[0046] Alternatively, there may be a specific algorithm used by thenetwork which can use geographical location information in order toselect the cell. The network can request the geographical informationfrom the mobile station or perform measurements in order to find out thelocation of the mobile station. In the GSM standard, there is a locationservices LCS feature This defines different methods for positioning amobile station. Altematively, the cell can be selected using somesubscriber specific data stored in the network, such as Support ofLocalised Service Area SoLSA information in which user specific cellgroups can be specified. These cells are called SoLSA cells and can beused for tariffing and/or for having different cell re-selectionbehaviour for different subscribers in the same area.

[0047] Once the cell with which the mobile station is to be associatedonce the connection has been released has been determined, this cellinformation is sent to the mobile station in step S4. In one preferredembodiment of the present invention, the cell information is included inthe connection release message. This message is the channel releasemessage in a GSM system and the radio resource control connectionrelease message in a UMTS system. The cell information is included in anoptional block with the connection release message. The content of thisoptional block may be subscriber specific. For example the SoLSAinformation can effect the content so that different subscribers can beordered to different cells or Radio Access Technologies RAT. Anothercase might be that all the roaming subscribers are, if possible, kept inGSM cells in the idle mode and only based on the requested servicehanded over to the UMTS cell. The non roaming subscribers may camp inany cell in idle mode.

[0048] In step S5 the mobile station releases the connection with thebase station or node B.

[0049] In step S6 the mobile station camps in the selected cell. Themobile station will periodically send messages to the base station ornode B of the selected cell and will periodically receive messages fromthe base station or node B of that selected cell. Messages may be sentonly if the location of the mobile station is changed. Alternatively,messages may be sent more regularly.

[0050] Reference will now be made to FIG. 5 which shows an alternativeembodiment of the invention. As mentioned previously, the method of FIG.5 may be used if it is decided that a mobile station is to camp on acell of the network to which the mobile station is not currentlyconnected. It should also be appreciated that the embodiment shown inFIG. 5 can also be used independently of the method shown in FIG. 4.

[0051] In step T1, the mobile station is initially in an idle state. Instep T2, the mobile station establishes a connection to a third party.

[0052] In the next step T3, a network element selects the network towhich the mobile station is to be associated when a connection has beenreleased. The network element can be the mobile services switchingcentre 12 or the base station controller 10 if the mobile station iscurrently connected to a base station of the GSM standard.Alternatively, if the mobile station is currently connected to node B ofa UMTS system, the radio network controller 16 or mobile servicesswitching centre 18 may make the decision. For example, all dual modemobile stations may always be ordered to a cell of a particular network.For example, a mobile station may always be ordered to a GSM cell.Alternatively, the network can be selected on the basis of the relativetraffic on the two networks, In order to make this selection, this willrequire some communication between the two networks. Yet anotherpossibility is that the selection of the cell may depend on theforecasted movement of the mobile station. For example, if the mobilestation on the basis of the measurement reports received seems to bemoving out of the coverage of the UMTS system, the mobile station may beordered to camp in the GSM system and listen to the signals of GSM basestations. The network, which is selected for camping, may be dependenton the coverage. For example, the mobile station will select theavailable network if only one network is provided in a particular area.

[0053] The mobile station may be ordered to camp in a cell of itscurrent location area or in a cell of a different location area. Thecell selection information for the mobile station may be accurate to acell, a location area, a frequency band, a network, or any other levelof accuracy.

[0054] Information on the network, which is selected, is sent to themobile station in the connection release message in step T4. This issimilar to the cell identity sent in the connection release message inthe embodiment of FIG. 4.

[0055] In step T5, the mobile station releases the connection. In stepT6, the mobile station selects the camping cell. The mobile station mayselect the cell based on measurements which it has made. In particular,the camping cell may be selected based on the measurement of signalsfrom a number of base stations. The base station which is received moststrongly is selected. Similarly if the network is the UMTS network, thenthe mobile station may consider the signals of node B. It should beappreciated that the mobile station may make new measurements or maymake the decision based on measurements made when the mobile station wasconnected to node B or the base station.

[0056] A third embodiment is described in FIG. 6. In the arrangementshown in FIG. 6, the message indicating the camping cell or the networkto be used is sent separately from the connection release message. Instep R1, the mobile station is initially in an idle state. In step R2,the mobile station establishes a connection to a third party. In stepR3, the connection release message is sent to the mobile station.

[0057] In step R4, the mobile station checks to see whether or not ithas received a message indicating the cell with which the mobile stationis to be associated once the connection has been released or thenetwork. In step R5, the connection is released by the mobile station.In step RB, if the message has been received, the mobile station isassociated with the identified cell. Alternatively, if the messageindicates the network, the mobile station will select the cell withwhich the mobile station is to be associated, as in the method of FIG.5. However, if the message is not received, the mobile station willremain associated with the cell with which it has just released theconnection.

[0058] It should be appreciated that the various steps shown in themethods of FIGS. 3, 4 and 5 can be performed in different orders tothose illustrated in the Figures. The mobile station is described asreleasing the connection. It is of course possible that the node B orbase station can control the release of the connection.

[0059] In embodiments of the present invention, when a connection isreleased, the mobile station is attached to the selected cell. This isunlike the prior art where the mobile station is attached to the cell towhich it was previously connected. In order to change the cell in theprior art, a cell selection procedure takes place.

[0060] Embodiments of the present invention are able to reduce therequired paging capacity. For example, if all the dual mode mobilestations are always associated with, for example a GSM cell after aconnection has been released, the GSM cells will not need to broadcastany UTMS cell information and paging messages for these dual modemobiles need not be sent on the UMTS network. It is of course possiblethat all dual mobile stations will always use the UTMS network.Accordingly in preferred embodiments of the present invention, onenetwork is preferred for camping, provided there is of course coverageby that network. In this way, a mobile station can be first paged on thepreferred network. However, it is possible in alternative embodiments ofthe present invention to page on both networks at the same time or topage on the different networks at different times. Location updates fora mobile station may be done when the system is changed, and thus thepage can be done to the system in which the mobile is camping.

[0061] The cell selection decision may use one or more of the followingpieces of information; the received measurement reports, in which casethe decision would usually be made by the BSC or radio networkcontroller, geographic location information, in which case a decisionmay be made in the MSC, BSC/RNC or SMLC (Serving Mobile LocationCenter). The decision may be based on cell information, again thedecision will be made either in the MSC or in the BSC/RNC. If thedecision is based on subscriber specific data, the decision may be madein the MSC and the BSC or radio network controller. The information onthe decided cell or network may be sent from the mobile servicesswitching centre to the base station controller or the radio networkcontroller and the information as to the cell or network may be includedin the call release message by the base station controller or the radionetwork controller. In different embodiments of the present invention,it is possible for any one or more elements of a network to make therequired decision.

[0062] Embodiments of the invention provide greater control over thenetworks. Different subscribers will have different needs. For examplesome subscribers may use mainly voice calls whilst others may almostentirely use video calls or data calls. The traffic load situations willdepend on these needs. Embodiments of the invention allow the networkoperator to optimise the call establishment traffic to take place in thenetwork which will be used in the actual call. The number of internetwork handovers can be reduced.

[0063] Embodiments of the present invention have been described ascontrolling the cell with which the mobile station is associated withafter a connection has been released. Embodiments of the invention canbe used when a mobile station is first switched on, prior to a callbeing established. This may be the case of the connection of thelocation update.

[0064] The mobile station can be any suitable user equipment and may bea mobile telephone, a portable computer or any other piece of wirelessequipment.

[0065] The default cell to be selected after channel release may beinstead of the same cell:

[0066] a different cell on the same network (on the same or on adifferent band); and different cell on another network.

[0067] The location area may be the same or a different one from -thearea of the released cell.

[0068] The cell selection information for the mobile station may beaccurate to a cell, a frequency band, a network, or the like.

[0069] The mobile station MS may, during a call, optionally be handedover to another cell (which may be on another location area compared tothe initial state cell or even on another network/system. In somespecial cases the location area could be the same in differentnetworks). Several hand overs may occur during the call. Then at thechannel release the mobile station MS may. optionally receive additionalinformation about the cell to be selected when entering again idle mode.

[0070] Embodiments of the invention may be useful when all mobiles areset to select for example, GSM in idle mode while they may use UMTS inconnected mode, or vice versa. Embodiments of the invention may beuseful also for example in a single band GSM system. For example,embodiments of the invention may be used in the case that the mobilestation MS is forwarded to a neighbouring cell with a directed retry ifthe camped cell has overload. Then at the channel release, assuming themobile station MS has not moved, the mobile station MS may be directlyassisted to select the cell it was camped on before the call. This againis useful in the case that the two cells are from a different locationarea when two unnecessary location updates may be avoided.

[0071] Reference will now be made to FIG. 7, which shows an alternativeembodiment of the invention. Aspects of this method may be used with themethods described earlier and vice versa.

[0072] In the first step W1, the mobile station receives from thenetwork a value. This value is a parameter which defines the preferredstatistical distribution of the mobile stations between two networks,systems or the like. This value is provided to the mobile station duringthe connection release signalling. The value is determined by thecontrollers of the two networks. Some networks or systems may have acommon controller. Each network can provide the same or different valuesto the mobile stations. In preferred embodiments, the mobile station isarranged to only one value from the network or system to which it isconnected during a call or the like. In one embodiment the value can bedefined as a value between 0 and 1. However, the range from which thevalue can be selected can take any other suitable values.

[0073] In the second step W2, the mobile station generates a randomnumber. The random number is selected from the same range from which thevalue is selected. Thus in one embodiment of the invention, the rangefrom which the random number is selected is between 0 and 1. Anysuitable method can be used to generate the random number.

[0074] In the third step W3, the mobile station compares the receivedparameter value with the random number generated. If the random numberis greater than the parameter, one network is selected whilst if therandom number is lower than the parameter the other network is selected.For example if the parameter has the value 0.3, the random number 0.2would result in one network being selected and if random number is 0.7then the other network would be selected. The result of this is thatbecause the mobile station generates the random number randomly,0.3×100, that is 30% of the time the one network is selected with theother network being selected (1−0.3)×100, that is 70% of the time.

[0075] In the fourth step W4, a cell in the selected network is campedon by the mobile station in its idle state. This involves the mobilestation identifying which cell of the selected network should be campedon.

[0076] It should be appreciated that a network can be selected forcamping only if there is a cell available. For example, at a givenlocation, only one network may be available and the mobile station willcamp on that network regardless of any statistical parameter. If amobile station is instructed to camp on a particular network and it isnot possible to camp on that network due to any reason, the mobilestation will camp on the other network.

[0077] In embodiments of the present invention it is possible to agreethat the border values of the parameter zone mean a forced selection.For example, the parameter may be defined by 3 bits which define 8values The first and last values result in a respective one of thenetworks being camped on. The intervening 6 values define statisticalvalues and are used in the same way as the statistical parameter asdescribed previously.

[0078] The parameter can be sent to the mobile station when a call isbeing released, when the channel used for the location area change basedlocation update is being released or at any other appropriate time. Inorder to prevent a plurality of inter system location updates, it may bepreferred not to provide the parameter when the first location updatesare made to the system. A similar operation can be achieved once a callhas been terminated in alternative embodiments of the present invention.

[0079] This embodiment has the advantage that the network is able tocontrol the paging and location update loads of the two networks orsystems. Embodiments of the invention have the advantage that thecontrol is easier for the networks or systems. This is because thenetworks or systems no longer need to make a decision on a mobilestation by mobile station basis but instead gives a statistical valuecommon for all the mobile stations or a subgroup of mobile stations suchas business users, a particular type of user or a particular type ofmobile station.

[0080] Thus in embodiments of the invention the network or networks maydetermine the plurality of cells on which the mobile station camps. Thedecision is thus made on the network side and not by the mobile station.The information defining which plurality of cells that mobile station isto be associated when idle is sent from the network to the mobilestation. This information is sent to the Mobile station in theconnection release signalling or message.

[0081] The parameter can be location dependent and take into account theloading conditions in the two systems. In alternative embodiments, theparameter may be location independent.

[0082] Embodiments of the present invention can be used where there aretwo or even more radio access techniques, such as GSM and UMTS.Embodiments of the present invention can be used where there are two oreven more frequency zones such as GSM 900 and GSM 1800. Embodiments ofthe present invention are particularly advantageous where the sameoperator controls both systems. However in alternative embodiments ofthe present invention, different operators may control the two systems.

[0083] Embodiments of the present invention can be used with more thantwo systems. For example, a first parameter can be sent which determineswhich radio access technique is to be used. A second parameter can alsobe sent which determines the frequency. Alternatively two or moreparameters can be sent which define ranges. For example, if theparameters a and b were sent to the mobile station, a random valuebetween 0 and a would select one system, a value between a and b wouldselect ;a second system and a value between b and 1 would select a thirdsystem.

1. A communications system comprising a first plurality of cellsoperating in accordance with a first mode and a second plurality ofcells operating in accordance with a second mode, each of said cellsbeing served by a respective first station, at least one second stationarranged to establish a connection with at least one first station, saidat least one second station being associated with said first pluralityof cells or said second plurality of cells during said connection andmeans arranged to send information to said second station for selectingwhich plurality of cells said second station is associated after saidconnection has been completed.
 2. A system as claimed in claim 1,wherein said selecting means is arranged to provide a statisticalparameter to said second station, said second station being arranged touse said parameter to determine which plurality of cells said secondstation is associated after said connection has been completed.
 3. Asystem as claimed in claim 2, wherein said second station is arranged togenerate a random number and to compare the random number with thestatistical parameter from which the plurality of cells with which saidsecond station is to be associated is determined.
 4. A system as claimedin claim 3, wherein the statistical parameter is selected from a firstrange of values and second station is arranged to generate the randomnumber from the first range of values.
 5. A system as claimed in anypreceding claim, wherein the selecting means is arranged to provide thesame statistical parameter to a plurality of second stations.
 6. Asystem as claimed in claim 5, wherein said selecting means is arrangedto provide the same statistical parameter to a subgroup of said secondstations, based on a characteristic associated with said secondstations.
 7. A system as claimed in any preceding claim, wherein an idlemode occurs after a connection has been completed.
 8. A system asclaimed in any preceding claim, wherein said first and second pluralityof cells are on different frequency bands.
 9. A system as claimed in anypreceding claim, wherein said first and second plurality of cells usedifferent radio access technology.
 10. A system as claimed in anypreceding claim, wherein said first and said second plurality of cellsare on different location areas.
 11. A system as claimed in anypreceding claim, wherein said first and second plurality of cells are ondifferent networks
 12. A communications system as claimed in anypreceding claim, wherein said second station is arranged to select acell of the selected plurality of cells.
 13. A communications system asclaimed in claim any preceding claim, wherein said second station usesmeasurements made during the connection to select a cell.
 14. Acommunications system as claimed in any preceding claim, wherein saidcommunications system is a wireless communications system.
 15. Acommunication system as claimed in any preceding claim, wherein saidfirst station is a base station.
 16. A communications system as claimedin any preceding claim, wherein said at least one second station is amobile station.
 17. A communications system as claimed in any precedingclaim, wherein said first and second plurality of cells use first andsecond standards respectively.
 18. A communications system as claimed inclaim 17, wherein one of said first and second standards is a frequencydivision multiple access standard.
 19. A communications system asclaimed in claim 17 or 18, wherein one of said first and secondstandards is a time division multiple access standard.
 20. Acommunications system as claimed in claim 17, 18 or 19, wherein one ofsaid first and second standards is a code division multiple accessstandard.
 21. A communication system as claimed in any of claims 17 to20, wherein one of said first and second standards is a GSM standard.22. A communications system as claimed in any of claims 17 to 21,wherein one of said first and second standards is a UMTS standard.
 23. Acommunications system as claimed in any preceding claim, wherein saidcommunications system comprises at least one network to which saidsecond station is attachable, said first stations being part of said atleast one network, wherein said at least one network is arranged todetermine the plurality of cells to which said second station is to beassociated.
 24. A communications system as claimed in claim 23, whereinsaid at least one network is arranged to provide information to saidsecond station defining the plurality of cells to which the secondstation is to be associated.
 25. A communications system as claimed inclaim 24, wherein said information is provided to said second station inassociation with connection release information.
 26. A communicationssystem comprising a first plurality of cells operating in accordancewith a first mode and a second plurality of cells operating inaccordance with a second mode, each of said cells being served by arespective first station, at least one second station arranged toestablish a connection with at least one first station, and meansarranged to send information to said second station for selecting whichat least one cell said second station is associated when said secondstation is idle.
 27. A communications system comprising a firstplurality of cells operating in accordance with a first mode and asecond plurality of cells operating in accordance with a second mode,each of said cells being served by a respective first station, at leastone second station arranged to establish a connection with at least onefirst station, said at least one second station being associated withsaid first plurality of cells or said second plurality of cells duringsaid connection and means arranged to send information to said secondstation for selecting if the second station is associated with at leastone cell operating in accordance with the first mode or at least onecell operating in accordance with the second mode, after said connectionhas been completed.
 28. A communications method for a communicationssystem comprising a first plurality of cells operating in accordancewith a first mode and a second plurality of cells operating inaccordance with a second mode, each of said cells being served by arespective first station, said method comprising the steps of:establishing a connection between a second station and at least onefirst station, said second station being arranged to receive informationfor selecting if the second station is to be associated with a celloperating in accordance with the first mode or the second mode;releasing the connection between the first and second station; andselecting if the second station is to be associated with a celloperating in accordance with the first mode or the second mode.
 29. Acommunications system method for a communications system comprising aplurality of cells, each of said cells being served by a respectivefirst station and at least one second station, said method comprisingthe steps of: establishing a connection between at least one firststation and a second station, said at least one second station beingassociated with a first cell during said connection; and means arrangedto send information to said second station for selecting which cell saidsecond station is associated with in idle mode after said connection hasbeen completed.
 30. A network element of a communications systemcomprising a plurality of cells, each of said cells being served by arespective first station, at least one second station arranged toestablish a connection with at least one first station, said at leastone second station being associated with a first cell during saidconnection, said network element comprising means arranged to sendinformation to said second station for selecting which cell said secondstation is associated with in idle mode after said connection has beencompleted.
 31. A first station of a communications system comprising aplurality of cells, each of said cells being served by a first station,at least one second station arranged to establish a connection with atleast one first station, said at least one second station beingassociated with a first cell during said connection, said first stationcomprising means arranged to send information to said second station forselecting which cell said second station is associated with in idle modeafter said connection has been completed.
 32. A second station of acommunications system comprising a first plurality of cells arranged tooperate in accordance with a first mode and a second plurality of cellsarranged to operate in accordance with a second mode, each of said cellsbeing served by a first station, said second station arranged toestablish a connection with at least one first station, said secondstation being associated with a first cell during said connection, saidsecond station being arranged to receive information for selecting whichplurality of cells said second station is associated.
 33. A secondstation as claimed in claim 32, wherein said information comprisesinformation on one or more of the following: cell; local area: radioaccess technology; network and band.
 34. A second station as claimed inclaim 32 or 33, wherein said information is received in association witha call release message.
 35. A communications system comprising aplurality of cells, each of said cells being served by a respectivefirst station; at least one second station arranged to establish aconnection with at least one first station; said at least one secondstation being associated with a first cell during said connection; andmeans arranged to send information to said second station for selectingwhich cell said second station is associated with in idle mode aftersaid connection has been completed.
 36. A system as claimed in claim 35,wherein said system comprises a first plurality of cells and a secondplurality of cells, said system selecting which plurality of cells thesecond station is associated in the idle mode.
 37. A communicationsystem as claimed in claim 35 or 36, wherein information identifying thecell with which the second station is associated in said idle mode isforwarded by the selecting means to said second station.
 38. Acommunications system as claimed in any of claims 35 to 37, wherein saidcell is selected based on one or more of the following: identity of thesecond station geographical location of said second station; measurementreports; cell information; and the capability of said second stationsuch as the frequency bands and/or radio access technologies the secondstation supports.
 39. A communication system as claimed in any of claims35 to 38, wherein said selecting means is arranged to send a message tosaid second station identifying if the second station is to beassociated with a cell of the first plurality of cells or a cell of thesecond plurality of cells.
 40. A communication system as claimed in anyof claims 35 to 39, wherein said selecting means is arranged to cause amessage to be transmitted to said second station indicating the cellsaid second station is to be associated and/or if the second station isto be associated with a cell of the first plurality or the secondplurality.
 41. A communication system as claimed in any of claims 35 to40, wherein in the absence of said message, said second station isarranged to be associated with the cell with which the second station isassociated with during the connection.
 42. A communication system asclaimed in claim 40 or 41, wherein said message is associated with aconnection release message
 43. A system as claimed in any of claims 35to 42, comprising at least one further network element, said networkelement comprising said selecting means.
 44. A system as claimed inclaim 40, wherein said network element comprises a mobile servicesswitching centre and/or a serving mobile location centre SMLC.
 45. Asystem as claimed in any of claims 35 to 44, wherein said selectingmeans is provided in said first station.
 46. A system as claimed inclaim 36, wherein the first plurality of cells is of a first network andthe second plurality of cells is of a second network.